This invention relates to testing and diagnostic systems of particular use in electronic devices such as computers. More specifically, the invention relates to an apparatus, method, and computer program product for detecting the presence of a mechanical component on a circuit board.
In addition to the electronic components in an electronic system such as a computer, the system may include a number of important non-electronic components. These non-electronic components are those having some function in the electronic system that does not necessarily depend upon receiving or sending an electrical signal, and will be referred to in this disclosure and the accompanying claims as xe2x80x9cmechanical components.xe2x80x9d
A heat sink is an example of a mechanical component commonly included in an electronic system. Heat sinks are devices used to help draw heat away from electronic components such as processors and transformers. The cooling provided by a heat sink is commonly critical to the proper operation of the electronic component with which the heat sink is associated. In fact, certain electronic components will overheat and become irreparably damaged if they are operated without a heat sink for a significant period of time.
Electronic systems may undergo various tests as part of the assembly and production process to determine the presence and proper operation of the various system components. Numerous electronic testing techniques have been developed for detecting and testing the operation of electronic components in an electronic system. However, testing for mechanical components requires different techniques.
One type of test arrangement which may be used for mechanical components includes an array of probes and switches. In this type of testing apparatus, the probe array is brought into contact with a surface of an electronic system such as a printed circuit board assembly while the system is held in a test fixture. When one of the probes reaches a location occupied by a mechanical component in the printed circuit board assembly, the contact between the component and the probe displaces the probe and this displacement is used to change the condition of a switch associated with the probe. The change in condition of the switch indicates that the mechanical component is present on the circuit board. However, if a probe which is aligned at a location of the board which is supposed to contain a mechanical component is not displaced as the probe array is brought into contact with the board assembly, the associated switch will not be tripped. This indicates that the mechanical component is not present at the desired position on the board.
Another type of test arrangement used in printed circuit board assembly testing includes one or more emitter/detector pairs. In emitter/detector type test equipment, an emitter emits a probe beam across an area of a printed circuit board assembly toward a detector adapted to detect the probe beam. If the probe beam is directed across an area in which a mechanical component is expected to be located, the detector should not detect the probe beam since it should be blocked by the mechanical component. If the probe beam is directed across an area that should contain a mechanical component but is detected by the detector, the presence of the probe beam at the detector indicates that the mechanical component is not present.
All of these prior test arrangements for mechanical components of an electronic system require special test fixtures adapted for the particular system under test. Also, testing may generally be done only at system assembly. Thus, the prior testing arrangements provide no method of detecting the presence of mechanical components once the assembly is put in service. However, a mechanical component such as a heat sink may be removed during system service or maintenance and may be inadvertently left off when the system is returned to service. With no way to test for the presence of the heat sink, the system may be allowed to operate without the heat sink for a period of time sufficient to damage the electronic component that the heat sink protected.
There is therefore a need for an improved testing arrangement for detecting the presence of mechanical components included in an electronic system. The improved testing arrangement should be useful not only during production testing but also after the electronic system is placed in service.
It is an object of the invention to provide an apparatus and method for facilitating the detection of a mechanical component on a substrate, particularly, a substrate such as a printed circuit board assembly of an electronic system. It is also an object of the invention to provide a computer program product for use in detecting the presence or absence of a mechanical component in an electronic system.
The apparatus according to the invention includes an electrically conductive strap which is used to secure a mechanical component in a desired position on a substrate. The strap is connected to an electrically conductive first connector at one end and connected to an electrically conductive second connector at the other end. Both connectors are mounted on the substrate so that the connected strap cooperates with the mechanical component to secure the mechanical component in the desired position. Also, the connection between the strap and the first connector electrically couples the strap to the first connector while the connection between the strap and the second connector electrically couples the strap to the second connector. At least one of the connectors, the first connector for example, is also electrically coupled to a first reference voltage preferably available on the substrate.
With this conductive strap and connector arrangement for securing the mechanical object on the substrate, the electrical condition of the second connector may be used to indicate whether the strap and therefore the mechanical component is in place on the substrate. That is, detecting the first reference voltage at the second connector indicates that the strap is properly connected between the first and second connectors and that the mechanical component is secured in place by the strap. However, detecting that the second connector is not electrically coupled to the first reference voltage indicates that the strap and mechanical component are both missing or are not properly installed.
The method according to the invention includes first coupling the first connector to the first reference voltage. The method then includes detecting the electrical condition of the second connector to determine if the second connector is electrically coupled to the first reference voltage (that is, to determine if the electrical condition at the second connector is affected by the first reference voltage). In a preferred arrangement, the first reference voltage comprises ground and the step of detecting the electrical condition of the second connector includes attempting to detect ground through the second connector.
Another important arrangement within the scope of the invention utilizes the logical state of a digital signal at the second connector to indicate the presence or absence of the strap and mechanical component. In this preferred form of the invention, the first connector is electrically coupled to ground while the second connector is coupled through a current limiting resistor to a supply voltage available on the substrate. In this arrangement, the second connector remains coupled to ground to produce a xe2x80x9clowxe2x80x9d or xe2x80x9c0xe2x80x9d logical state at the second connector when the strap is in place securing the mechanical component in the desired position. Thus, detecting a logical xe2x80x9c0xe2x80x9d at the second connector indicates the presence of the strap and the mechanical component. However, if the strap is removed so that it no longer holds the mechanical component in the desired position, the second connector is then no longer coupled to ground and is pulled up to the supply voltage level through the current limiting resistor to produce a logical xe2x80x9chighxe2x80x9d or xe2x80x9c1xe2x80x9d at the second connector. Detecting a logical xe2x80x9c1xe2x80x9d at the second connector thus indicates that the strap and mechanical component are absent.
The method of detecting the presence of a mechanical component on a substrate according to the invention may be performed as part of the initial product testing and may also be performed after the system is placed in service. Furthermore, one preferred form of the invention tests for the presence of the mechanical component as part of the system startup or boot sequence. In this form of the invention, a logic device is coupled to read the signal state at the second connector. During system startup, status inquiry program code causes the logic device to read the logical state at the second connector. If the logic device reads a logical xe2x80x9c0xe2x80x9d then the strap and mechanical component are considered in place and operational control program code causes the system to assume a normal operational state. However, if the logic device reads a logical xe2x80x9c1xe2x80x9d at the second connector, then the strap and mechanical component are considered not present. In this case the operational control program code causes the system or a portion of the system to go into a safe operation mode to ensure no damage occurs to electronic components due to the absence of the mechanical component. Also, the operational control code may produce an error message indicating that the mechanical component may not be present in the system.
The apparatus and method according to the invention simply and reliably detects the presence or absence of mechanical components on a substrate such as a printed circuit board assembly. Also, the invention facilitates not only production testing but also facilitates testing for the presence or absence of mechanical components after the system has been placed in service.
These and other objects, advantages, and features of the invention will be apparent from the following description of the preferred embodiments, considered along with the accompanying drawings.